Pre-formed inserts for use with concrete structures are known. The inserts are typically incorporated into the structure during concrete pouring to facilitate attachment of threaded fasteners, such as bolts and the like.
Prior art inserts include internally threaded barrels which are tensioned axially by an attached bolt. The prior art insert also include a base at a distal end of the barrel. The base extends outwardly from the barrel to embed the insert within a concrete structure and increase the force necessary to pull the insert out of the concrete structure. The prior art insert further includes tapering ribs connected to the base and to an outer surface of the barrel to strengthen the base.
Prior art inserts, initially made of metal, have also been made from injection molded thermoplastic (acetal) materials. The inserts are made in a variety of sizes for receiving bolts of various diameters, such as ¼″, ⅜″, ½″, ⅝″, ¾″, 1″, 1½″, for example. The metal and plastic inserts of the prior art are similar in construction. The plastic prior art inserts, however, stretch to a greater extent than the corresponding metal inserts because of increased elongation properties of plastic compared to steel. As the barrel of the plastic insert stretches, the reinforcing ribs become wedged against the concrete. Resulting failure of the plastic inserts short of the base creates a smaller shear cone compared to that created by a comparably sized metal insert, which undesirably equates to a lower pull out force for the prior art plastic insert.